This application claims the priority of PCT/EP99/00880 filed Feb. 10, 1999 and German patent document 198 06 687.2, filed Feb. 18, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a braking apparatus for preventing a collision of a vehicle with an obstacle, such as another vehicle located to its front, in which a collision message and/or braking operation is triggered as a function of the headway between the vehicle and the obstacle, the difference in speeds of the vehicle and of the obstacle (relative speed) and also the speed and acceleration or deceleration of the vehicle.
A method of this type may be found, for example, in U.S. Pat. No. 4,073,359, in which data detected by sensors is used to determine whether the vehicle moving at the measured speed and deceleration can still come to a stop in front of the obstacle; that is, within a distance smaller than the headway between the vehicle and the obstacle. If not, an imminent collision is signaled.
In this case, however, neither vehicle-relevant data, such as, for example, the loading state, nor environment-relevant data, such as, for example, the state of the road, are taken into account. Furthermore, there is also no account taken of the driving situation in which the vehicle finds itself.
It has been shown in the past, in particular, that, in the case of heavy commercial vehicles, for example heavy-goods vehicle convoys, or articulated vehicles or in the case of buses, the most frequent type of accident involves a crash into the back of the next heavy-goods vehicle in a line of traffic on the highway. According to representative statistics, no braking maneuver takes place in approximately 40% of these accidents. Even where coaches are concerned, accidents involving rear-impact crashes on motorways often lead to many people being injured or killed. In this case, too, according to representative statistics, there is no braking maneuver in approximately 30% of the accidents.
The apparent reason for such failure to apply the brakes is that vehicles which are stopping or moving slowly are overlooked or not recognized by the driver due to inattention, fatigue or the like. Another cause of accidents is that the vehicle""s own speed is not adjusted accordingly when visibility is poor or in darkness. Further causes of accidents are that passing is not possible, for example, when the passing lane is occupied, that the speed of vehicles, particularly those leading on a hill, is wrongly estimated, or that the prescribed safety headway of successive vehicles is not maintained.
Furthermore, in many cases, braking maneuvers in lines of traffic lead to a so-called concertina effect, the result of which is that less reaction and stopping distance is available to the drivers of other following vehicles at an increasing distance of the vehicle from the first braking vehicle.
German patent document DE 42 44 183 C2 discloses a device for assessing a possible collision of a vehicle with an obstacle, in which the travel of a vehicle and the travel of the obstacle are estimated in advance and, when there is the risk of a collision, a collision avoidance mechanism is triggered. In this case, the position which the vehicle would assume and the position which the obstacle would assume after a predeterminable time interval has elapsed are precalculated. The collision avoidance mechanism includes an alarm and a hydraulic generator which can actuate the brakes of the vehicle. This device ignores the activity of the vehicle driver. The actuation of the alarm means and the actuation of the hydraulic generator in a critical situation take place even when, for example, the driver has already taken countermeasures to prevent a collision.
One object of the invention is to provide a method for preventing a collision of a vehicle the above generic type, in which particularly in a line of traffic, a collision message or a braking operation is triggered only from that moment when a collision or an accident involving a rear-impact crash cannot be avoided either by braking or by the vehicle being steered past the obstacle. The method is also to take into account, in particular, the activity of the driver; that is, countermeasures already initiated in a hazardous situation.
This and other objects and advantages are achieved by the collision avoidance method and apparatus according to the invention, in which in addition to the signals detected as above, the driver""s activity (particularly accelerator pedal actuation, brake pedal actuation, actuation of the direction indicator and/or the degree of steering lock), the state of the road, the loading state and the degree of overlap of the vehicle relative to the obstacle, are detected. Based on this information, a first headway between the vehicle and the obstacle is calculated, which is the least necessary to make it possible to avoid a collision with the obstacle by means of a braking operation with maximum deceleration. A second headway is calculated, which is the least necessary to make it possible to avoid a collision with the obstacle by steering the vehicle past the obstacle; and automatic braking is initiated only when the detected headway is smaller than both the first and the second calculated headway.
When driver activity takes place, the braking operation can be initiated in the case of a smaller detected or actual headway. At the same time, in an advantageous embodiment of the method, the first headway between the vehicle and the obstacle and the second headway which is necessary to make it possible to avoid a collision with the obstacle by the vehicle being steered passed the obstacle are reduced by a predeterminable amount when:
a) the vehicles still half overlap one another;
b) the direction indicator is actuated and the accelerator pedal is actuated up to a predeterminable threshold value;
c) the direction indicator is actuated and a predetermined steering angle is exceeded; or
d) the brake pedal is actuated up to a predeterminable threshold value.
In all these cases, there is driver activity which implies that either the driver is overcoming a critical driving situation by his own activities or there is no critical driving situation present at all.
Preferably, at the same time, the vehicle is braked with maximum deceleration until the relative speed assumes the value zero.
Moreover, there may advantageously be provision for the brake lights of the vehicle to be switched on before the automatic braking operation is initiated. As a result, the driver of a following vehicle is informed at an early stage of the initiation of the braking manoeuver necessary for overcoming the critical driving situation.
The invention also provides a braking device for a vehicle, comprising at least one sensor for detecting the speed and acceleration/deceleration of the vehicle, at least one sensor for detecting the headway between the vehicle and an obstacle located in front of the vehicle, preferably another vehicle traveling in front of the vehicle, and the difference in speeds of the vehicle and of the obstacle (relative speed), and also a central control unit which automatically actuates a brake as a function of the signals detected by the sensors. In addition, at least one sensor is provided for detecting the driver""s activity (in particular accelerator pedal actuation, brake pedal actuation, actuation of the direction indicator and/or the degree of steering angle lock), as well as at least one sensor for detecting the degree of overlap of the vehicle relative to the obstacle, at least one sensor for detecting the loading state and at least one sensor for detecting the state of the road. The output signals from these sensors are supplied to the central control unit for triggering a braking operation and calculating a maximum braking deceleration as a function of the signals emitted by the sensors, when the headway detected by the sensors for detecting the headway between the vehicle and the obstacle located in front of the vehicle is smaller than both a first calculated headway between the vehicle and the obstacle, which is at least necessary to make it possible to avoid a collision of the vehicle with the obstacle by means of a braking operation with maximum deceleration, and a second calculated headway, which is at least necessary to make it possible to avoid a collision of the vehicle with the obstacle by steering the vehicle past the obstacle, and when the degree of overlap detected by the sensors for detecting the degree of overlap exceeds a predetermined threshold.
In an advantageous embodiment, at least one sensor is provided for detecting the headway and the relative speed between the vehicle and an obstacle located in front of the vehicle and the at least one sensor for detecting the degree of overlap to be two radar sensors arranged, spaced apart, on the front side of the vehicle. In this case, these radar sensors can, in a particularly advantageous way, simultaneously assume the function of the sensor for detecting the headway and the relative speed and of the sensor for detecting the degree of overlap.
In order, in particular, to make it possible for the brake to have a very fast response behavior, the brake is advantageously an electronically activatable compressed-air brake.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.